A scroll type fluid machine having a bypass hole structure is disclosed in Japanese Patent Publication No. 2-55636, for example. In the scroll type fluid machine disclosed in this gazette, symmetrical fluid working chambers of two systems are formed between a pair of scrolls having symmetrical shapes, and bypass holes are provided in these fluid working chambers of the respective systems.
FIG. 5 illustrates sectional views of the pair of scrolls of the aforementioned conventional scroll type fluid machine. The scroll type fluid machine comprises a non-revolving scroll F and a revolving scroll O. First fluid working chambers A are formed between an inner surface Fa of a spiral blade of the non-revolving scroll F and an outer surface Ob of a spiral blade of the revolving scroll O, and second fluid working chambers B are formed between an outer surface Fb of the spiral blade of the non-revolving scroll F and an inner surface Oa of the spiral blade of the revolving scroll O. Bypass holes AH and BH are provided in correspondence to these fluid working chambers A and B of two systems respectively.
One bypass hole AH is that making outer peripheral side first fluid working chambers A1 to A3 communicate with a low-pressure port L, and the other bypass hole BH is that making outer peripheral side second fluid working chambers B1 to B3 communicate with the low-pressure port L. The two bypass holes AH and BH open and close at the same timing through bypass valves respectively. Work (a compression step in case of a compressor) can be started from inner peripheral side first fluid working chambers A4 to A6 and second fluid working chambers B4 to B6 by providing the bypass holes AH and BH, and a working fluid is discharged to a high-pressure port H in a state reducing the capacity.
In the conventional scroll type fluid machine shown in FIG. 5, the bypass holes AH and BH are provided in correspondence to the respective fluid working chambers A and B respectively. Further, the bypass valves and operating pressure mechanisms operating these bypass valves are also necessary in two sets respectively in correspondence to the two bypass holes AH and BL, and working portions increase in number as a whole, while the number of parts also increases. Thus, the machine becomes inferior in manufacturability and reliability.
In order to solve the aforementioned problem, it is conceivable, not to provide bypass holes in correspondence to the respective fluid working chambers A and B respectively, but to provide a single large bypass hole. For example, it is conceivable to provide a large bypass hole CH shown by phantom lines in FIG. 5. In case of providing the single large bypass hole CH in the conventional scroll type fluid machine shown in FIG. 5, it comes to that the inner peripheral side second fluid working chamber B4 which must work at an angle of rotation within the range of 0 to .pi. radian about .pi./2 radian inevitably communicates with the low-pressure port L. Therefore, the single bypass hole CH cannot be provided in the conventional scroll type fluid machine shown in FIG. 5.
In other words, the conventional scroll type fluid machine comprising the pair of scrolls having the shapes shown in FIG. 5 is forced to be provided with the two bypass holes AH and BH. It is apprehended that the working fluid leaks from peripheral portions of the two bypass holes AH and BH in full-load driving closing these two bypass holes AH and BH. When such leakage takes place, loss of the performance increases. When a liquid refrigerant of a non-compressive fluid or oil gets mixed into the fluid working chambers in large quantities, if a lag is caused in the timing for opening the two bypass holes AH and BH, and if the volume of the operating pressure chamber for the bypass valve opening earlier reduces, the pressure in the operating pressure chamber for the bypass valve delayed in opening operation increases, the opening operation is further delayed, and discharge of the liquid cannot be smoothly performed.